Various arrangements for automatic irrigation of potted plants are well known in the art. U.S. Pat. No. 3,753,315 is illustrative of a double pot system in which an aperture is located on or near the bottom of an inner pot and a sponge located between the bottom of the inner container and above the inside bottom of an outer container. Water is transferred from the outer container to a cavity containing the sponge and, through capillary action, the water moves upwardly from the sponge through the aperture in the inner pot to moisten the plant soil. One problem associated with such a device has been the difficulty of controlling the amount of water transferred to the plant. Quite often such types of planters have not proved satisfactory as soil often becomes water saturated and causes rotting of the plant roots. U.S. Pat. No. 3,552,058 illustrates another form of double pot system in which a mass of earth provides the function of the sponge in the aforementioned U.S. Pat. No. 3,753,315.
Another form of automatic watering device is shown in U.S Pat. No. 4,825,591 in which a plant hangs from one end of a vertical rod with a spring at the opposite end of the rod for actuating a valve in a water tank. As the soil dries and becomes lighter, the spring lifts the plant and triggers a water tank valve to open and water the plant. The complexity of this apparatus makes it unsuitable for greenhouse use where multitudes of plants are growing. Furthermore, the complexity of the apparatus makes it susceptible to high failure rates and its size and complexity are not cost effective for mass watering.